This invention relates to processes for making rheology modifiers. More particularly, the invention relates to processes for making urethane rheology modifiers especially useful in water-based and organic solvent-based compositions.
Additives have long been used in coating compositions for various purposes. Thus, viscosity control agents, surfactants, sag-control agents, anti-foaming agents and other materials are added to coating compositions in minor amounts for their respective functions. Rheology modifiers are also added to such compositions not only for increasing the viscosity of the coating composition but to maintain the viscosity at desired levels under varying process conditions and end-use situations. Secondary effects obtained from the rheology modifiers include protective colloidal action, improvement in pigment suspension, leveling and flow. Some of these properties are also desired in similar type compositions, for instance textile treating compositions, cosmetics, paper compositions, well drilling, fire-fighting foams, detergents, pharmaceuticals, agricultural formulations, and emulsions of all kinds. It can be seen rheology modifiers are used in a variety of compositions.
Many well-known rheology modifiers are used with varying degrees of success. Thus, natural products such as the alginates, casein, and gum tragacanth and modified natural products such as methyl cellulose and hydroxyethyl cellulose are useful rheology modifiers. Synthetic rheology modifiers have also been used. These materials include the carboxyvinyl ether copolymers, acrylic polymers and maleic anhydride/styrene copolymers.
U.S. Pat. No. 4,079,028 describes rheology modifiers which are said to be useful in latex paints. The described modifiers have hydrophobic tails and their molecular structure can be linear, branched or star-shaped. The branched modifiers have been found to be particularly useful; however the disclosed process for making them is somewhat cumbersome in that it is necessary to remove the solvent medium in which they are made, physically break up the modifiers and redisperse them in a solvent compatible with the latex paint.
There has now been found processes for making rheology modifiers of the type described in U.S. Pat. No. 4,079,028 by convenient and economical processes. The modifiers obtained by these processes are in a fluid form which can be readily added to latex paints without a consequent compatibility problem.
As used herein, all percents and ratios are by weight unless otherwise stated.